Electromagnetic reed relay having metal foils underneath and above the excitation winding



' M r 8, 1969 v. MENGELBlRG 3,

ELECTROMAGNETIC REED RELAY HAVING METAL FOILS UNDERNEATH AND ABOVE THEEXCITATION WINDING Filed March 15. 1967 INVENTOR V MEN 65!. 85R 6 BY MWATTORNEY United St2lt8 Patent 7 Claims ABSTRACT OF THE DISCLOSURE Forspark quenching, i.e. for damping the switch-01f voltage peaks atterminals of the excitation winding of a relay, several layers ofelectrically and/or magnetically conductive metal foils are arrangedunderneath as well as above the excitation winding.

The invention relates to an electro-magnetic relay with reed contactsthe excitation winding of which is surrounded by a magneticallyconductive envelope consisting of a wrapping-like ribbon which can bemagnetized in the direction of the magnetic field produced by anexcitation coil. The ribbon serves simultaneously to shield againstexternal magnetic fields and to couple the magnetic field produced bythe excitation coil to the reed contacts.

A similar relay is shown in the German patent specification No.1,071,231. In that relay a cover layer surrounding the excitationwinding serves to conduct the intrinsic magnetic field and to shield thereed contacts against external magnetic fields.

However, in relays with reed contacts still other difficulties occurwhich must be dealt with constructively with regard to switching. Inparticular, spark quenching is important for such relays, because relayswith reed contacts contain only a little conductive material withinwhich short-circuits can be formed. The contact elements themselvesrepresent the only current paths which may contribute to a damping. Butthese elements are small and their extension in the direction of theattenuating current is low. Moreover, the material used is selectedaccording to its magnetic properties and badly conducting, which meansit is most unsuitable for attenuation. Consequently, the switch-offpeaks of the voltage at the coil terminals are high, even if they are ofshort duration.

For a better understanding of this problem the conditions forconventional relays will be explained first. Standard-type flat relaysand many other relays contain an iron core, an iron armature and an ironyoke, being sufliciently conductive for induction currents to damp theswitch-01f peaks of the voltage at the coil terminals. Only coilsbearing much energy, as for example, selector coils, must be equippedwith attenuating or damping elements against switch-off voltage peaks.

Moreover, it is known that relays, the dropping period of which isdelayed by electrical means, require no spark quenching through dampingelements, because damping is performed by the delay elements. Theeffects are the same with regard to the electrical conditions, becauseall damping elements have the same effect; they let coil current flow toa certain extent, perhaps only in one lane inductively coupled with thewinding (short-circuit winding). The efiect is that the dissolution ofthe flux in the coil does not exceed a predetermined voltage value. Asecondary effect can thereby not be avoided without particular measures,viz that the armature excitation drops also slower as would be the caseat a complete and sudden switch-0E. Consequently, it is substantiallyunimpor- "ice taut, whether the damping is achieved by a short-circuitpath within the relay, its coil or by an external damping arrangementconsisting of diode and resistor or capacitor and resistor; all sucharrangements cause a certain delay of the relay in pulling up and/ordropping.

In relays with reed contacts, for constructive reasons, damping currentpaths are not provided. Therefore, redays with reed contacts must beequipped generally with spark quenching facilities. This may be providedconventionally by a series-connection of a blocking diode and a resistorarranged in parallel to the excitation coil. These spark quenchingelements are arranged on a conductor plate and connected through wireswith the relays, mounted at another place. Conventional spark quenchingwith capacitor, and resistor (RC-elements) requires too much spaceforrelay circuits of this type.

It is an object of the invention to reduce the customary expenditure forspark quenching in reed contact relays. This is achieved, according tothe invention, by damping the switch-off peaks at the terminals of theexcitation winding through several layers of electrically and/ ormagnetically conductive metal foil arranged underneath the excitationwinding as well as above the excitation winding.

According to an embodiment of the invention, the foil windings on theexcitation winding consist entirely or partly of several layers of barecopper foil.

According to a further embodiment of the invention the foil windingsunderneath and above the excitation winding consist entirely or partlyof several layers of conductive, soft ferromagnetic foil.

The influence of the envelope in extending the pull up and droppingperiods of the relay is reduced, according to a further embodiment ofthe invention in that the foil Winding located underneath the excitationwinding has an annular recess in the area of the operating air gaps ofthe reed contacts.

According to a further embodiment of the invention, a magneticallyinsulating intermediate piece of insulating foil may be wound into saidannular recess.

In order to provide additional damping paths the head pieces or disksmay consist, according to a further embodiment of the invention,entirely or partly of copper and/or of another, also ferromagnetic,electrically conductive metal, insulated by lacquering or by a foil.

Recently electrical coils became known which are wound similarly tocapacitors, on one-side of an insulated foil, preferably aluminum foil.The German printed application 1,202,902 shows such a coil of ananodized aluminum foil.

Compared with the prior art, a particular advantage of an embodiment ofthe present invention is that the excitation winding of the relay iswound of a metal ribbon, insulated on one side. In this case the entirecoil, i.e. the. foil winding arranged underneath the excitation winding,the excitation winding itself, consisting of a metal ribbon, and theshielding foil winding on top of the excitation winding is madepreferably in one single continuous work process on a winding machine.

An electro-magnetic relay constructed in accordance with the inventionpossesses various advantages. For example, the saving in work, materialand space is considerable due to the elimination of the conventionalspark quenching elements. Since the relay itself is only a little moreexpensive than the arrangements known without damping windings and thesavings in expenditure and Work substantially outweighs these smalladditional costs the relay represents an exceptionally economicalcomponent. If the entire coil of the relay is made of foil material theparticular advantage is obtained that the relay can be manufactured witha tool, similar to that to wind capacitors, immediately after the reedcontacts have been 3 made. Such a machine can produce the relayaccording to the invention completely automatically, ready forinstallation.

The invention is described with the aid of a drawing which shows anexample of the relay according to the invention.

The magnetizable top shielding layer 1 is wound of several layers offoil, not being insulated on one side, but which is bare and has propercontact to both adjacent layers. The pole pieces 2 and 3 underneath theexcitation winding 4 are wound of the same material and in the same way.Between the pole pieces 2 and 3 a short path remains magnetically openaround the air gap 5 of the reed contacts 6 and 7, which path is filledwith insulating foil 8. The excitation winding 4 may consist of aconventional wire winding or may be wound, preferably, of a metal ribboninsulated on one side which insulation somewhat projects at the edges.The head pieces 9 and 10' of the coil are also made of metal andmagnetically conductive.

A thermoplastic layer underneath the pole pieces 2 and 3, athermoplastic insulation of the metal ribbon of the excitation winding4, and a thermoplastic covering foil can be polymerized in a heatingprocess, assembling the entire relay to a compact unit. The projectingends of the insulation of the excitation winding 4 are thereby glued tothe head pieces 9 and 10.

If the attenuation or damping windings 1, 2 and 3, and the head pieces 9and 10 consist of copper, the entire coil canbe soldered to withstandtropic climates.

The entire circular conductivity of the various current paths can easilybe dimensioned so that a switch-off peak voltage at the terminals of theexcitation winding 4 of e.g. 100 to 250 volts is not exceeded whichotherwise would become dangerous for contacts and semi-conductors.

While the principles of the invention have been described above inconnection with specific apparatus and applications, it is .to beunderstood that this description is made only by way of example and notas a limitation on the scope of the invention.

What is claimed is:

1. An electro-magnetic relay with reed contacts including an excitationcoil surrounded by a magnetically conductive envelope, the envelopeincluding a foil wrapping wound to be magnetizable in the direction ofthe magnetic field produced by said excitation coil, the toil wrappingproviding shielding against external magnetic fields and leading themagnetic field produced by said excitation coil to the reed contacts,wherein the improvement comprises means for damping switch-off voltagepeaks at the terminals of the excitation coil including several layersof electrically and magnetically conductive bare metal foil arrangedunderneath as well as above said excitation coil.

2. An electro-magnetic relay according to claim 1, in which the foilwinding consists of several layers of bar copper foil.

3. An electro-magnetic relay according to claim 1, in which the toilwindings, arranged underneath and above the excitation winding, consistof several layers of conductive, soft ferromagnetic foil.

4. An electro-magnetic relay according to claim 1, in which the foilwinding underneath the excitation Winding is wrapped at either end of anannular recess in the area around an air gap between the reed contacts.

5. An electro-magnetic relay according to claim 4, in which a magneticalinsulating intermediate piece of insulating foil is Wound into theannular recess of the bottom foil winding.

6. An electro-magnetic relay according to claim 1 in which, in order toprovide additional damping paths, head pieces are provided at eachenvelope, each head piece consisting of ferromagnetic, electricallyconductive metal.

7. An electro-magnetic relay according to claim 1, in which theexcitation winding of the relay is wound of a metal ribbon, insulated onone side.

References Cited UNITED STATES PATENTS 5/1967 Morrison 335-151 7/1968Young 33684 US. Cl. X.R.

